[mrb]

Hum, no. Sandy/Ivy Bridge can only execute 4 double-precision instructions per cycle per core, in the form of two SSE instructions per cycle (one instruction doing adds, the other doing muls, executed by different units).

Doing 8 double-precision instructions per cycle would translate to either four 128-bit SSE instructions, or two 256-bit AVX instructions per cycle, which is not possible (unless I did not keep track of the latest AVX capabilities).